Estimate Impact With a Baseline, Not a Vibe

worked-trail comparison-spectrum before-after Signup conversion rose from 8.0% before launch to 8.6% after launch. Did the homepage cause a 0.6-point lift? Observed change minus credible counterfactual equals impact. A before-after difference assumes the homepage was the only meaningful change. Traffic mix changed, so that assumption is weak. Step 1 Observed change = 8.6% - 8.0% = +0.6 percentage points. This is the visible movement, not yet causal impact. Step 2 Check mix: paid-search share rose from 20% to 42%. A higher-converting channel can lift overall conversion without the homepage helping. Step 3 Compare within channel: paid search 10.2% -> 10.1%;…

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